Just some thoughts...

From what I've read, he went down one wrong trail and then turned onto another wrong trail. He seemed to realize by the end of Sunday that he was lost and stopped traveling. He had to ration food and did have a nearby water source of some sort. It sounds like he had a filter for water purification, maybe tablets too and of course fire. I hear rumors there may be been a group communication issue as well.

What he did right
1. realized he was lost and stopped
2. stayed calm
3. stayed warm (temps not bad)
4. stayed hydrated
5. rationed food
6. finally decided to use fire as signal

What he did wrong
1. took wrong turn (happens to most at some point)
2. walked too far without making sure he was following trail markers; did the side trails have the same markers?

What he could change
1. get a PLB since he travels alone and is visually challenged
2. get a gps and use it with a UTM gridded map; even if you walk off the edge of a paper map, with known coordinates you know about how many kilometers off you are and in what direction
3. do not solo backpack